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Reproduction is a biological process by which living organisms produce new individuals of their own kind. It is essential for the continuity of species and maintenance of population. Although reproduction is not necessary for the survival of an individual, it is vital for the survival of a species. For NEET aspirants, reproduction in organisms is a fundamental and conceptual chapter of Class 12 Biology.
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Life span refers to the period from birth to natural death of an organism. Different organisms have different life spans, ranging from a few days to several years.
Examples:
Butterfly – few weeks
Dog – 10–15 years
Elephant – 60–90 years
Banyan tree – hundreds of years
Life span is genetically determined and influenced by environmental factors. Understanding life span helps in studying reproductive maturity and reproductive cycles.
Reproduction is broadly classified into two main types:
Asexual reproduction
Sexual reproduction
Asexual reproduction involves the formation of offspring without the fusion of gametes. The offspring produced are genetically identical to the parent and are called clones.
Modes of Asexual Reproduction:
1. Binary Fission:
Occurs in unicellular organisms like Amoeba and Paramecium, where the parent cell divides into two identical daughter cells.
2. Multiple Fission:
Seen in Plasmodium, where the nucleus divides repeatedly before cytoplasmic division.
3. Budding:
Occurs in Hydra and yeast, where a small outgrowth develops into a new individual.
4. Fragmentation:
Seen in organisms like Spirogyra, where the body breaks into fragments that grow into new individuals.
5. Regeneration:
Planaria and Hydra can regenerate lost body parts to form a complete organism.
Asexual reproduction is rapid and energy efficient but does not produce genetic variation.
Sexual reproduction involves the formation and fusion of male and female gametes to form a zygote. It leads to genetic variation, which is essential for evolution.
Key Features of Sexual Reproduction:
Involves meiosis
Fusion of gametes (fertilization)
Formation of zygote
Development of embryo
Sexual reproduction occurs in plants, animals, and humans.
Sexual reproduction occurs in three phases:
1. Pre-fertilization Events:
Includes gametogenesis and gamete transfer. Gametogenesis involves the formation of haploid male and female gametes through meiosis.
2. Fertilization:
Fusion of male and female gametes to form a diploid zygote. Fertilization may be internal or external.
3. Post-fertilization Events:
Includes zygote formation, embryogenesis, and development of new organism.
Organisms adopt different reproductive strategies to ensure survival of their species.
Examples:
High number of gametes in organisms with external fertilization
Fewer but well-protected offspring in organisms with internal fertilization
Some organisms reproduce only once in their lifetime (semelparous), while others reproduce multiple times (iteroparous).
Parthenogenesis is a special type of reproduction where the embryo develops from an unfertilized egg. It is seen in honey bees, ants, and some reptiles. This topic is important from the NEET point of view.
Reproduction plays a crucial role in:
Continuity of species
Maintaining population balance
Introducing genetic variation
Evolution and adaptation
Without reproduction, life would not continue on Earth.
| Feature | Asexual Reproduction | Sexual Reproduction |
|---|---|---|
| Gamete formation | Absent | Present |
| Genetic variation | No | Yes |
| Rate | Fast | Slow |
| Energy requirement | Low | High |
| Evolution | Not promoted | Promoted |
This chapter is highly important for NEET because:
It builds the base for human reproduction and reproductive health
Many direct NCERT-based questions are asked
Diagrams and definitions are frequently tested
A strong understanding of basic concepts helps in scoring full marks from this unit.
Reproduction ensures species continuity
Asexual reproduction produces clones
Sexual reproduction introduces variation
Fertilization leads to zygote formation
Life span varies among organisms
Reproduction in organisms is a fundamental biological process essential for the survival and evolution of life. Understanding the types, mechanisms, and significance of reproduction is crucial for NEET aspirants. With well-structured notes and concept clarity, students can easily score high in this chapter. StudentBro.in provides reliable, exam-focused NEET Biology notes to make learning simple and effective.
